EP-A-0559105 discloses a storage box which consists of a holder containing a plurality of retaining slots arranged side-by-side to receive screwdriver bits. A hinged lid is pivotally connected to the bit holder. If the capacity of the storage box needs to be increased, the volume of the storage box must be increased which makes it inconvenient to carry. In addition, the hinged lid is provided with a keyhole perpendicular to the rotary axis and the bit holder slides in the keyhole to prevent or allow rotation. However the keyhole is defined in such a way that it further increases the volume of the storage box.